This invention relates to electric machines with magnetic cores made of amorphous metal ribbon, and more particularly to utilization of the amorphous metal material required for the magnetic circuit to serve also as the plate material of an integral capacitor.
Most single-phase motors use a capacitor for starting, running, or both, and this is required in order to achieve the required phase shift between main and auxiliary starting currents. The cost of this capacitor may in some cases exceed the cost of the base motor. There are other situations where a capacitor is associated with a motor or generator, such as for power factor correction or for filtering rectified power. In all of these cases the capacitor is normally a discrete component.
Motors and inductive components having laminated magnetic cores made from long lengths of amorphous metal ribbon, either toothed or with a uniform width, are a recent development in the art. Amorphous metals are also known as metallic glasses and exist in many different compositions including a variety of magnetic alloys which include iron group elements and boron or phosphorous. Metallic glasses are formed from metal alloys that can be quenched without crystallization, and these materials are mechanically stiff, strong and ductile, and are low cost. The ferromagnetic types have very low coercive forces and high permeabilities and are especially attractive because of their low losses. Ribbons of the Fe.sub.80 B.sub.20 alloy have one-fourth the losses, at a given induction for sinusoidal flux, of the best oriented Fe-Si steel. Additional information is given in the article "Potential of Amorphous Metals for Application in Magnetic Devices" by F. E. Luborsky et al, Jr. of Applied Physics, 49(3), Part II, March 1978, pp. 1769-1774.
Amorphous metal is manufactured by extruding the melt under pressure onto a rapidly rotating very cold chill surface, and the liquid alloy is changed into a solid ribbon in a short time measured in micro-seconds before it becomes crystalline. The cooling rate is in the order of 10.sup.6 .degree. C./sec. The maximum ribbon thickness at present is two mils or less; the thickness limitation is set by the rate of heat transfer through the already solidified material, which must be rapid enough that the last increment of material still avoids crystallization. The inherently thin nature of this material and the large number of motor laminations that are needed-punched steel strip is commonly 10 mils or greater in thickness--is one of the assumed disadvantages of using amorphous metal alloys in electric motors.